1. Field of the Invention
The present invention relates to a stop determination apparatus for determining whether a vehicle such as an automobile is at a standstill, an inclination determination apparatus for determining an inclination of the road surface on which the vehicle such as an automobile is stopped, and an electric parking brake controller which incorporates both these apparatuses.
The present application claims each priority from Japanese Patent Application Nos. 2006-001667, 2006-051635, and 2006-274991, the respective disclosures of which are incorporated herein by reference.
2. Description of the Related Art
An electric parking brake actuates a parking brake during vehicle parking or stopping using, for example, an electric actuator such as a motor. Such an electric parking brake can be operated by a vehicle operator using electrical switches, thus allowing reduced operator efforts when compared to a manual lever or foot brake pedal.
It has also been suggested that the electric parking brake be provided with an additional hill-hold (hill-holder) function. The hill-hold function serves to automatically actuate the electric parking brake when the vehicle is stopped on an inclined road surface, in order to prevent unintentional movement of the vehicle. To fully realize such a hill-hold function, a reliable determination must be made as to whether the vehicle is at a standstill.
Vehicles are known which are provided with a vehicle speed sensor for detecting the rotational speed of the drive wheels and which utilize its output for determination of a stop of the vehicle. However, such a vehicle speed sensor cannot accurately detect the speed of the vehicle running at an extremely low speed immediately before the vehicle is being stopping. For example, it may be impossible to detect when the vehicle is running at an actual speed of about 2 km/h or less. In this regard, one type of conventionally known electric parking brakes is configured so that a timer is activated when the vehicle speed sensor detects a speed of 2 km/h or less immediately before the vehicle is stopped. Then, the vehicle is determined to be at a standstill after a predetermined period of time has elapsed, and the brakes are applied (for example, see Japanese Patent Application Laid-Open Publication No. 2004-142517).
However, with this conventional technique, the determination of a stop of the vehicle is made only on the basis of this elapsed period of time after the vehicle speed cannot be detected. This may readily allow a difference between the time at which the vehicle is actually brought to a standstill and the time at which the vehicle is determined to be at a stop. The difference would in turn sometimes result in the electric parking brake being activated even when the vehicle has not yet actually stopped. Conversely, the difference would also sometimes allow the vehicle to start to roll onward after the vehicle has been stopped due to a time lag between the stop thereof and the activation of the electric parking brake. This time lag might, for example, be up to about 2 seconds, and thus needs to be improved.
Furthermore, using this conventional technique, it is difficult to accurately estimate the timing of a stop. If any acceleration of the vehicle unexpectedly occurs after the vehicle is determined to have stopped, a G sensor (acceleration sensor), which is normally used to determine the inclination of a road surface, would detect this acceleration and incorporate it into an erroneous determination of the inclination of the road surface.
Furthermore, different braking forces are required for the hill-hold function depending on the inclination (slope) of a road surface on which the vehicle is stopped. For example, on a steep hill, a larger braking force is required to prevent unintentional movement of the vehicle. However, producing such a larger braking force every time would cause an increased burden on the device under normal conditions of use as well as an increase in the power required for activation. In regard to this, an electric parking brake is also known which is provided with an inclination sensor for detecting the inclination of a road surface with an acceleration (G) sensor, to change the braking force in response to the output therefrom (for example, see aforementioned Japanese Patent Application Laid-Open Publication No. 2004-142517).
However, during deceleration of the vehicle or immediately after a stop of the vehicle, the inclination sensor using the G sensor will detect a deceleration G or a longitudinal G caused by pitching of the vehicle or the like, and thus cannot properly determine the inclination. Thus, this will cause a time lag of, for example, about 2 seconds after the vehicle has stopped before the determination of the inclination can be completed. This in turn will cause a time lag between the stop of the vehicle and the activation of the electric parking brake. Thus, for example, after the vehicle has been stopped on an inclined road, the user must keep the brake pedal depressed for a period of time corresponding to this time lag. Thus, further improvement in operability is desired.